Wake simulator

ABSTRACT

1. An electronic device for simulating wakes of submarines or other underwater targets comprising: FIRST CIRCUIT MEANS FOR PROVIDING A SERIES OF OUTPUT SIGNALS REPRESENTATIVE OF SEA BACKGROUND AND A TRIGGERING PULSE PRIOR TO EACH OF SAID SIGNALS; SECOND CIRCUIT MEANS RECEIVING SAID TRIGGERING PULSES FROM SAID FIRST CIRCUIT FOR GENERATING IN RESPONSE THERETO RECTANGULAR PULSES HAVING THE TRAILING EDGES THEREOF OCCURRING COINCIDENT IN TIME WITH CORRESPONDING ONES OF SAID SEA BACKGROUND SIGNALS; THIRD CIRCUIT MEANS RECEIVING THE OUTPUT OF SAID SECOND CIRCUIT MEANS FOR FILTERING THE SAME AND PROVIDING OUTPUT SIGNALS INDICATIVE OF THE WAKE OF THE TARGET, SAID WAKE SIGNALS HAVING COINCIDENCE IN TIME WITH CORRESPONDING ONES OF SAID SEA BACKGROUND SIGNALS; AND FOURTH CIRCUIT MEANS RECEIVING SAID SERIES OF SEA BACKGROUND SIGNALS AND SAID WAKE SIGNAL FOR ADDING THE SAME AND FOR PROVIDING A COMPOSITE SIGNAL REPRESENTATIVE OF A TARGET WAKE SUPERIMPOSED ON THE SEA BACKGROUND.

United States Patent Ter eluk Au 28 1973 [54] WAKE SIMULATOR EXEMPLARYCLAIM [75] Inventor: Paul Terpeluk, l-lorsham, Pa. 1. An electronicdevice for simulating wakes of subma- 7 Assigmw The United states ofAmerica as rines or other underwater targets comprising:

Filed:

represented by the Secretary of the Navy, Washington, DC.

July 30, 1965 Appl. No.: 476,787

Primary Examiner-T. H. Tubbesing Attorney-G. J. Rubens, Henry Hansen andJ. A.

Cooke first circuit means for providing a series of output signalsrepresentative of sea background and a triggering pulse prior to each ofsaid signals;

background signals; and

fourth circuit means receiving said series of sea background signals andsaid wake signal for adding the same and for providing a compositesignal representative of a target wake superimposed on the seabackground.

in time with 10 Claims, 2 Drawing Figures PLAYBACK UNIT OSCILLOSCOPEPATENTEDAUBZMQH 3.7554607 30 4 ,1 VARIAB v BLE 9 A P BA PASS A GENE TORFILTER g PLAYBACK ADDER 9 UNIT AMPLBIFIER r L I o @J g. 1 60/OSCILLOSCOPE L L k L i L i \r M 2 INVENTOR.

PAUL TERPELUK ATTORNEYS WAKE SIMULATOR The invention described hereinmay be manufactured and used by or for the Government of the UnitedStates of America for governmental purposes without the payment of anyroyalties thereon or therefor.

The present invention relates to electronic simulation equipment andmore particularly to electronic equipment for simulating a wake of asubmarine or other moving underwater targets.

In the development of antisubmarine warfare infrared detectionequipment, studies of the recognizability of submarine wakes as afunction of sea background conditions are required. Heretofore,photographs of actual infrared submarine wakes under various sea stateshave been recorded on magnetic tape for later play back on anoscilloscope. Obviously, the variations in infrared wakes as against seastates, will be limited to the number of tape recordings obtained. Inaddition to the use of wake recognizability in antisubmarine warfaresystem studies respecting the utility of various types of infrared linescan equipment, the wake recognizability is important as a trainingdevice for familiarizing infrared operators with submarine wakerecognition techniques.

The wake simulator of the present invention synthesizes submarine wakesfor superimposition on magnetic recordings of various sea states. Thus,an infinite number of variations in wake characteristics can besuperimposed on various sea state conditions. Briefly, this isaccomplished by providing a tape playback unit for producing a number ofseries of electrical output signals representative of a selected seastate background, each series being preceded by an electrical triggeringsignal, by providing a serially connected variable pulse generator andvariable bandpass filter responsive to the triggering signal forproducing an electrical waveform representative of the wake to besimulated, and by providing electrical signal summing apparatus forsuperimposing the wake signal upon the sea background signal to producea composite electrical signal representative of the wake in theenvironment of the selected sea state background.

It is, therefore, an object of the present invention to provide anelectronic simulator for simulating submarine or other underwater targetwakes.

Another object of the present invention is to provide an electronicdevice for simulating infrared wakes on various sea states.

A further object of the present invention is to provide an electronicdevice for simulating unlimited variations of infrared submarine wakeson an unlimited number of sea states.

A still further object of the present invention is to provide anelectronic device for synthesizing submarine wakes for superposition onvarious sea states for studying the utility of various types of infraredline scan equipment and for use as a training device for familiarizinginfrared operators with submarine wake recognition techniques.

A still further object of the present invention is to provide anelectronic wake simulator wherein the wakes can be presented on aselected background in various orientations, intensities and shapes.

Various other objects and advantages will appear from the followingdescription of an embodiment of the invention, and the novel featureswill be particularly pointed out hereinafter in connection with theappended claims.

ln the drawing:

FIG. 1 is a block diagram of an embodiment of a wake simulator systemaccording to the invention, and

FIG. 2 is a graphical presentation of representative signals through thewake simulator.

Ordinarily, a navigable body of water does not have a completelyhomogeneous temperature distribution. For example, it is well known thatwater at various depths may have differing temperatures which vary inaccordance with temperature gradients. Further, it is known that variousportions of the surface water have different temperatures. Sensitiveinfrared apparatus has been developed for sensing these differingtemperatures and making successive, geographically displaced scans ofthe surface of the water to obtain for each scan an outputrepresentative of the variation in temperature over the surface alongthe scan path. A visual representation of the distribution oftemperatures over the surface of the water may be obtained in a wellknown manner by simultaneously displaying successive scans in thegeographical order in which they were taken.

It is known that when a ship or submarine passes over or near thesurface of a body of water the existing pattern of distribution of thevarious surface temperatures is disturbed. This disturbancecreates adistinguishable infrared trace which is commonly thought to be left byreason ofa mixing of water of differing temperatures at and adjacent thesurface thereof. After a period of time, this infrared trace tends todissipate as the surface of the water gradually assumes a distributionof temperatures similar to that of the contiguous surface water. Atfirst, the width of the infrared trace or wake is usually primarilyeffected by the type of vessel which created the wake. For example, asnorkling submarine usually has been found to leave a much narrowerinfrared wake than does a surfaced submarine, the two wakes beingcompared after the same period of time. With the passage of time, theinfrared wake at a given location usually tends to become wider. Ofcourse, the width of the infrared wake displayed relative to the seastate background depends upon the relative geographical excursion of aparticular scan in addition to the above discussed relative width of thepath of interference of the vessel. The intensity of the wake commonlytends to be affected by the sea state and by the passage of time; Theforegoing are only representative of a number of possibilities forexplaining the appearance of the infrared wake upon a sea statebackground as represented by a discontinuity in the distribution oftemperature differentials.

In an exemplary embodiment according to the invention, a video taperecording of a particular sea state condition obtained during a priormission and including triggering pulses thereon immediately prior intime to the video pulses is played back through a tape playback unit 20and provides the input for simulator circuit 10. It should be noted herethat although an actual video recording of a particular sea state isutilized to provide the video input to the simulator circuit 10, thesame effect can be alternatively obtained by the use of a random pulsegenerator or the like to provide the background input waveforrns similarto that illustrated in line D of FIG. 2. The waveforms of line D, aremerely representative of a distribution of varying water temperaturesalong a line scan. It is helpful to visualize the representativewaveforms on line D as being used to intensity modulate a horizontalline scan of an oscilloscope. For example, the troughs of the waveformmay be visualized as points of light having varying degrees ofbrightness, and the intervening peaks may be visualized as points ofdarkness. If successive packets in the waveform are simultaneouslydisplayed in geographical order as by being used to intensity modulatesuccessive vertically displaced horizontal line scans, a distribution ofpoints of light is obtained which is or simulates an infrared picture ofthe body of water scanned. Of course, some of the points of light havingthe same brightness may be grouped together to represent water havingessentially the same temperature. It is upon this composite distributionof temperatures representing an infrared sea state condition that thesimulation of an infrared wake as made by a vessel is to besuperimposed.

The trigger pulse output, illustrated in line A of FIG. 2 and obtainedfrom the playback unit 20, is applied to a variable pulse generator 30of conventional design and configuration which generates a series ofperiodic rectangular pulses (see line B of FIG. 2) since the triggeringis periodic. Both the amplitude and width of these rectangular pulsesmay be controlled by the pulse generator and the adjustment may beperformed either manually or automatically. These rectangular pulsesfrom pulse generator 30 are then supplied as an input to a conventionalvariable bandpass filter 40 wherein a wake of different shapes is formedby varying the filter bandpass settings. See line C of FIG. 2.

'It is well known that a rectangular pulse has a complex frequencydistribution including high and low frequency components. It is furtherwell known that a high pass filter by definition will sharply attenuatelow frequencies. Hence, the output waveform of a high pass filter havinga rectangular pulse input can be made to resemble the differentiation ofthe rectangular pulse. Conversely, the output of a low pass filterhaving a rectangular pulse input can be made to resemble the integrationof the input pulse since the high frequencies are sharply attenuated.Since a bandpass filter has output characteristics of both low and highpass filters, the shape of the output thereof in response to arectangular pulse input will resemble that of a waveform which liesbetween complete differentiation and complete integration of arectangular pulse. Hence it follows that by selectively varying thebandpass and band width characteristics of a variable bandpass filter,the output thereof in response to the input of rectangular pulses may becaused to resemble spikes of selectively varied widths, shapes anddegrees of sharpness.

It may be seen from lines B and C of FIG. 2 that the leading edge spikeat the output of the filter 40 will be fixed while the trailing edgespike will vary with the input pulse width. Since the width andamplitude of the square wave output of the pulse generator 30 may bevaried continuously during the operation so as to achieve the desiredorientation of the wake relative to the sea scene obtained by the videooutput of the recorder and since the width and shape of the trailingedge spike may be altered, a wake can be presented in differentorientations, intensities and shapes.

The output of filter 40 (line C of FIG. 2) is then supplied as the inputto an adder and amplifier 50. The

6 video signal (line D of FIG. 2) from the tape playback unit 20 is alsosupplied as an input to the adder and amplifying circuit 50 where it isadded to the filter signal.

The output of circuit 50 is supplied to a monitor such as anoscilloscope where the composite waveform, (line E of FIG. 2) is used tointensity modulate the scope. The oscilloscope 60 has the horizontalsweep circuit initiated by the trigger pulse or sync pulse output ofplayback unit 20 and has a free running vertical sweep. It isunderstood, of course, that the output of adding and amplifying circuit50 may be used with devices other than the oscilloscope withoutdeparting from the scope or spirit of the present invention.

In operation, a video tape of a prerecorded sea state or the randomnoise generator is operated and settings are made on both the pulsegenerator 30 and the bandpass filter 40 to obtain the desiredorientation, shape and intensity of the wake. For example, the wake maybe presented at an angle to the sea scene display by adjusting the pulsegenerator to continuously vary the rectangular pulse width. Such anarrangement is illustrated in lines B and C of FIG. 2 where it isobserved that the trailing edge spike of the filter output (which formsthe wake on the display) varies with the width of the input pulse. Onthe other hand, the wake can be displayed vertically on the sea scene bycontrolling the pulse output from the pulse generator 30 at a constantwidth. In each case, it should be noted, the shape of the wake per semay be controlled by the setting of the filter 40. The output of thefilter 40 is superimposed on the sea state video output of the videotape and the composite waveform is used to intensity modulate thedisplay 60.

It will be understood that various changes in the details, materials,steps and arrangements of parts which have been herein described andillustrated in order to explain the nature of the invention may be madeby those skilled in the art within the principle and scope of theinvention as expressed in the appended claims.

What is claimed is:

I. An electronic device for simulating wakes of submarines or otherunderwater targets comprising:

first circuit means for providing a series of output signalsrepresentative of sea background and a triggering pulse prior to each ofsaid signals; second circuit means receiving said triggering pulses fromsaid first circuit for generating in response thereto rectangular pulseshaving the trailing edges thereof occurringcoincident in time withcorresponding ones of said sea background signals;

third circuit means receiving the output of said second circuit meansfor filtering the same and providing output signals indicative of thewake of the target, said wake signals having coincidence in time withcorresponding ones of said sea background signals; and

fourth circuit means receiving said series of sea background signals andsaid wake signal for adding the same and for providing a compositesignal representative of a target wake superimposed on the seabackground.

2. The device as defined in claim 1 wherein said first circuit meansincludes a playback unit for transmitting a series of video outputsignals from a prerecorded video tape of said sea background.

3. An electronic device for simulating wakes of submarines or otherunderwater targets comprising:

first circuit means for providing a series of output signalsrepresentative of sea background and a series of triggering pulsesoccurring prior to each series of said sea background signals;

second circuit means receiving said series of triggering pulses fromsaid first circuit for generating a series of rectangular pulses thirdcircuit means receiving the output of said second circuit means forfiltering the same and providing output signals indicative of the wakeof the target;

fourth circuit means receiving said series of sea background signals andsaid wake signal including means for adding the same and for providing acomposite signal representative of a target wake superimposed on the seabackground, said fourth circuit means further including an amplifiercircuit for amplifying said composite signal.

4. An electronic device for simulating wakes of submarines or otherunderwater targets comprising:

first circuit means including a playback unit for transmitting a seriesof video output signals representative of sea background from aprerecorded video tape of said sea background, said first circuit meansfurther including means for providing a series of triggering pulsesoccurring prior to each series of said sea background video outputsignals;

second circuit means receiving said series of triggering pulses fromsaid first circuit for generating a series of rectangular pulses, saidsecond circuit means further including means for varying the amplitudeand width of said rectangular pulses;

third circuit means receiving the output of said second circuit meansfor filtering the same and providing output signals indicative of thewake of the tarfourth circuit means receiving said series of seabackground signals and said wake signal for adding the same and forproviding a composite signal representative of a target wakesuperimposed on the sea background.

5. The device as defined in claim 4 wherein said second circuit means isa variable pulse generator.

6. The device as defined in claim 5 wherein said third circuit means isa variable bandpass filter.

7. The device as defined in claim 6 further including display meansreceiving said composite signal from said fourth circuit means.

8. The device as defined in claim 7 wherein said display means is anoscilloscope which is intensity modulated by said composite signal andtriggered by said triggering pulses.

9. An electronic device for simulating infrared wakes comprising:

first circuit means for providing a series of output signalsrepresentative of infrared background and a triggering pulse prior toeach of said background signals; second circuit means receiving saidtriggering pulses from said first circuit for generating in responsethereto a series of rectangular pulses, the trailing edges thereofhaving coincidence in time with corresponding ones of said backgroundsignals; third circuit means receiving the output of said second circuitmeans for filtering the same and providing output signals indicative ofthe infrared wake, said wake signals having coincidence in time withcorresponding ones of said background signals; and fourth circuit meansreceiving said series of background signals and said wake signal foradding the same and for providing a composite signal representative ofan infrared wake superimposed on the infrared background. 10. Anelectronic device for simulating wakes comprising:

first circuit means for providing a series of output signalsrepresentative of background and a series of triggering pulses; secondcircuit means receiving said series of triggeringv pulses from saidfirst circuit for generating a series of rectangular pulses ofselectively variable widths and amplitudes; third circuit meansincluding selectively variable bandpass filter means receiving theoutput of said second circuit means for filtering the same and providingin response to the trailing edge of said rectangular pulses outputsignals indicative of the wake and having coincidence in time withrespective ones of said background signals; and fourth circuit meansreceiving said series of background signals and said wake signal foradding the same and for providing a composite signal representative of aselectively variable wake superimposed in a selectively variableposition on the background.

1. An electronic device for simulating wakes of submarines or otherunderwater targets comprising: first circuit means for providing aseries of output signals representative of sea background and atriggering pulse prior to each of said signals; second circuit meansreceiving said triggering pulses from said first circuit for generatingin response thereto rectangular pulses having the trailing edges thereofoccurringcoincident in time with corresponding ones of said seabackground signals; third circuit means receiving the output of saidsecond circuit means for filtering the same and providing output signalsindicative of the wake of the target, said wake signals havingcoincidence in time with corresponding ones of said sea backgroundsignals; and fourth circuit means receiving said series of seabackground signals and said wake signal for adding the same and forproviding a composite signal representative of a target wakesuperimposed on the sea background.
 2. The device as defined in claim 1wherein said first circuit means includes a playback unit fortransmitting a series of video output signals from a prerecorded videotape of said sea background.
 3. An electronic device for simulatingwakes of submarines or other underwater targets comprising: firstcircuit means for providing a series of output signals representative ofsea background and a series of triggering pulses occurring prior to eachseries of said sea background signals; second circuit means receivingsaid series of triggering pulses from said first circuit for generatinga series of rectangular pulses third circuit means receiving the outputof said second circuit means for filtering the same and providing outputsignals indicative of the wake of the target; fourth circuit meansreceiving said series of sea background signals and said wake signalincluding means for adding the same and for providing a composite signalrepresentative of a target wake superimposed on the sea background, saidfourth circuit means further including an amplifier circuit foramplifying said composite signal.
 4. An elecTronic device for simulatingwakes of submarines or other underwater targets comprising: firstcircuit means including a playback unit for transmitting a series ofvideo output signals representative of sea background from a prerecordedvideo tape of said sea background, said first circuit means furtherincluding means for providing a series of triggering pulses occurringprior to each series of said sea background video output signals; secondcircuit means receiving said series of triggering pulses from said firstcircuit for generating a series of rectangular pulses, said secondcircuit means further including means for varying the amplitude andwidth of said rectangular pulses; third circuit means receiving theoutput of said second circuit means for filtering the same and providingoutput signals indicative of the wake of the target; fourth circuitmeans receiving said series of sea background signals and said wakesignal for adding the same and for providing a composite signalrepresentative of a target wake superimposed on the sea background. 5.The device as defined in claim 4 wherein said second circuit means is avariable pulse generator.
 6. The device as defined in claim 5 whereinsaid third circuit means is a variable bandpass filter.
 7. The device asdefined in claim 6 further including display means receiving saidcomposite signal from said fourth circuit means.
 8. The device asdefined in claim 7 wherein said display means is an oscilloscope whichis intensity modulated by said composite signal and triggered by saidtriggering pulses.
 9. An electronic device for simulating infrared wakescomprising: first circuit means for providing a series of output signalsrepresentative of infrared background and a triggering pulse prior toeach of said background signals; second circuit means receiving saidtriggering pulses from said first circuit for generating in responsethereto a series of rectangular pulses, the trailing edges thereofhaving coincidence in time with corresponding ones of said backgroundsignals; third circuit means receiving the output of said second circuitmeans for filtering the same and providing output signals indicative ofthe infrared wake, said wake signals having coincidence in time withcorresponding ones of said background signals; and fourth circuit meansreceiving said series of background signals and said wake signal foradding the same and for providing a composite signal representative ofan infrared wake superimposed on the infrared background.
 10. Anelectronic device for simulating wakes comprising: first circuit meansfor providing a series of output signals representative of backgroundand a series of triggering pulses; second circuit means receiving saidseries of triggering pulses from said first circuit for generating aseries of rectangular pulses of selectively variable widths andamplitudes; third circuit means including selectively variable bandpassfilter means receiving the output of said second circuit means forfiltering the same and providing in response to the trailing edge ofsaid rectangular pulses output signals indicative of the wake and havingcoincidence in time with respective ones of said background signals; andfourth circuit means receiving said series of background signals andsaid wake signal for adding the same and for providing a compositesignal representative of a selectively variable wake superimposed in aselectively variable position on the background.